1. Field of the Invention
This invention relates generally to electrical energy generation, and more particularly to the generation of electrical energy from wind energy.
2. Description of the Prior Art
With the energy crisis facing most industrialized countries of the world brought about by the increasing scarcity and rapidly escalating cost of oil and natural gas, utility companies have realized that alternative sources to oil and natural gas of electrical power generation must be developed and utilized. Such alternative sources, such as nuclear, hydro-electric power generation, solar power generation and wind power generation must be developed and utilized.
However, because of the increasing public outcry as to further reliance on nuclear power generation, that alternative is becoming increasingly a less viable alternate to fossil fuel power generation. Hydro-electric generation is limited to geographical areas with sufficient water resources to operate such facilities and solar power generation technology has not advanced to a state where it would lend itself to generation of sufficient power to supply the present critical needs.
In 1972 the Solar Energy Panel of the National Science Foundation and the National Aeronautics and Space Administration estimated that there are 100,000 gigawatts of recoverable wind energy in the United States alone. This is one hundred times as much electrical power as is estimated to be required in the United States in 1980.
There is a cubic relationship between wind speed and power, that is power is proportional to wind speed cubed. Wind speeds increase logarithmically with height and over a level area the wind at an elevation of 220 feet will blow 1.27 times as fast as at a 50 foot elevation. Because of the cubic relationship between power and wind speed the power available from the wind at the 220 foot elevation would be 2.051 times as great as the power available at the 50 foot elevation.
Thus, it has been proposed to attempt to harness the tremendous energy present in the wind to generate electrical energy. Such prior proposals to harness wind energy have centered around variations of the windmill to capture the wind energy. Recent developments in this area are reflected by the proposed ERDA-NASA wind turbine which mounts a variable pitch propeller of about 125 feet in diameter on a fixed tower 100 feet in height.
As presently designed, the ERDA-NASA wind turbine operates at a constant speed of 40 rpm in wind speeds between 6 and 60 mph with the turbine blades being fully feathered in wind speeds above 60 mph. The rotor, transmission, generator and controls of the ERDA-NASA wind turbine are mounted on a rotatable bedplate at the top of the 100 foot high tower. Torque is transmitted from the rotor hub to the electrical generator through a gear box with a speed ratio of 45 to 1. Rated capacity of this unit is rated at 100 KW in an 18 mph wind. This type of wind turbine sacrifices power output at wind speeds greater than 18 mph because at higher wind speeds the rotor is maintained at 40 rpm by varying the pitch of the rotor blades to maintain the constant rated power output of 100 KW. Power is also sacrificed at wind speeds less than 18 mph by changing generator loadings to maintain the rotor turning at the required 40 rpm.
In addition, wind tunnel tests suggest that the minimum permissible spacing required between adjacent ERDA-NASA type wind turbines to prevent interaction of the rotors is ten times the rotor diameter. With a rotor diameter of 125 feet the minimum spacing between adjacent units would be 1,250 feet. At that spacing, at an average power output of 100 KW each, to produce 100 magawatts of rated power capacity would require an area of about 90 square miles.
Thus, it is evident that for large power requirements the ERDA-NASA type wind turbine is not a viable solution because of the large land mass needed to sustain a wind turbine farm. In addition, capital costs of construction are high.